Fluorinated elastomeric copolymers



United States Patent M 3 318,854 FLUORTNATED ELASTOMERIC CGPOLYMERS Francis J. Honn, Boston, Mass, and Willard M. Sims, Hacircnsaclr, N.J., assignors, by mesne assignments, to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Original application Apr. 3, 1953, Ser. No. 346,800, new Patent No. 2,965,619, dated Dec. 20, 1960. Divided and this application Feb. 5, 1960, Ser.

12 Claims. (Cl. zen-87.7

This invention relates to the crosslinking of fluorinated, linear, saturated polymers and, more particularly, to the vulcanization of fiuorinated, linear, saturated elastomers.

This application is a division of our prior and copending application Ser. No. 346,800, filed Apr. 3, 1953, now U.S. Patent 2,965,619.

Linear or chain polymers are thermoplastic in nature. They exhibit continuous flow under the influence of heat and pressure. Such polymers can be resoftene'd as often as desired and are usually soluble in selected solvents. Some chain polymers are elastomeric in nature, that is to say, they stretch readily under external tension and retract rapidly and completely on release of tension.

Vulcanized or cross linked elastomers may have equal, greater, or lesser extensibility than the linear elastomers, depending on the number and nature of the crosslinkages. In any case, they have lessened plasticity and solubility and increased toughness and heat resistance.

Fluorinated thermoplastic resins have been found to be extremely useful in cases where chemical inertness, thermal stability and/ or electrical insulation properties are desirable. Fluorinated el-astomers are useful in any situation where elastomers are used and Where chemical inertness and/or electrical insulation properties are desired. Many of these elastomers possess the additional advantage of retaining their elastomeric properties over a greater temperature range than previously known elastomers.

It is an object of this invention to crosslink fluorinated, linear, saturated elastomers.

It is a further object of this invention to prepare soft vulcanizates of fluorinated, linear, saturated elastomers of increased toughness and heat stability but unreduced or even superior extensibility.

It is a further object of this invention to produce hard thermosetting vulcanizates of fiuorinated, linear, saturated elastomers.

It is a further object of this invention to reduce the solubility of fluorinated, linear, saturated elastomers produced by the copolymerization of at least two mono-olefinic compounds.

It is a further object of this invention to produce tough, chemically inert coatings from solutions of fluorinated, saturated, linear elastomers.

Other objects will appear hereinafter.

These and other objects are accomplished by the following invention. Linear elastomers comprising disordered, saturated, fiuorinate'd carbon chains, and including a substantial number of carbon atoms which are linked only to hydrogen and to other carbon atoms, are reacted with a crosslinking agent at elevated temperatures to produce a vulcanized elastomer. Ordinarily, the linear elastomer is at least percent comprised of -CH groups.

Disorder in the linear, saturated, fluorinated carbon chains is ordinarily achieved by the copolymerization of at least two mono-olefinic compounds. In order to obtain chemical stability in the elastorner, at least one of the mono-olefinic compounds must be flnorinated. In order that the copolymer be elastomeric in nature, at least one of the mono-olefinic compounds must contain at least one carbon atom linked only to hydrogen and carbon atoms.

3,318,854 Patented May 9, 1967 At least 10 percent of the carbon atoms in the chain must be of this type in order to obtain an elastomeric product. Ordinarily, a mono-olefinic compound containing a CH group is used and this results in the linear chains containing CH groups. When the mono-olefinic compound contains an unsaturated chain of three or more carbon atoms, methyl groups may be present and these remain as side groups on the linear chain.

Among the fluorinated mono-olefinic compounds which may be used as cornonomers to produce fluorine-containing elastomers are:

CH C Fa These fluorinate'd mono-olefinc compounds may be copolymerized with each other, provided at least one of the cornonomers contains at least one carbon atom bonded only to hydrogen and carbon atoms. Fluorinated olefinic compounds, such as those listed above, may also be copolymerized with other mono-olefinic compounds supplying the carbon atoms which are linked only to hydrogen and carbon atoms. Among the mono-olefinic compounds which may be used for this purpose are vinyl chloride, propylene, styrene, vinylidene chloride, acrylonitrile, nbutyl acrylate, divinyl benzene, ethylene, acrylamide and vinyl bromide.

Among the copolymer systems which are particularly advantageous are the following:

vinylidene fluoride-1,lchlorofluoroethylene vinylidene fiuoridetetrafluoroethylene vinylidene fluoride-bromotrifluoroethylene vinylidene fluoride2-chloroperfluoropropylene vinylidene fluoride-acrylamide vinylidene fluoride-chlorotrifluoroethylene difluorodichloroethylene (asym.)vinylidene chloride dichlorodifiuoroethylene (asym. )-n-butyl acrylate perfiuoropropylene-l, l-fiuorochloroethylene n-butyl acrylate-l,l-difluoro-2-chloroethylene n-butyl acrylate-tetrafluoroethylene trifluoroethylene-l 1 -fluorochloroethylene 1,l-fluorochloroethylene-Z-chloroperfluoropropylene tetrafluoroethy1ene-ethylene tetrafluoro ethylene-l l-fluorochloroethylene The copolymerization reaction may be carried out in either a Water suspension type system or in a mass polymerization system. In the former system the reaction is preferably carried out at a temperature between about 0 C. and about 35 C. In a mass polymerization system the reaction is preferably carried out at a temperature between about 20 C. and about C. With the water suspension type system a redox catalsyt system is preferred. It has and contains an oxidant, a reductant and a variable valence metal salt. The oxidant in the water suspension type recipe is preferably an inorganic persulfate, such as potassium persulfate, sodium persulfate or ammonium persulfate, the latter being most desirable. The reductant is preferably a bisulfite, such as sodium bisulfite or potassium bisulfite, and preferably the former. The variable valence metal salt which is employed for the purpose of regenerating the oxidant is preferably in the form of an iron salt, such as ferrous sulfate or ferrous nitrate with ferrous sulfate being the most desirable variable valence metal salt.

In the mass polymerization system, organic peroxide promoters, and particularly halogen-substituted acyl peroxide, are used. Trichloroacetyl peroxide is a preferred promoter of this type. Other halogen-substituted organic peroxides suitable for carrying out the polymerization are trifluoroacetyl peroxide, difluoroacetyl peroxide, 2,4- dichlorobenzoyl peroxide, chloroacetyl peroxide, trifluorodichloropropionyl peroxide, and dichlorofluoroacetyl peroxide.

By the method of this invention these rubbery copolymers may be transformed into soft vulcanizates of increased strength and toughness, of decreased solubility and of the same or increased extensibility or alternatively they may be transformed into hard vulcanizates which are thermosetting. The crosslinking agents used to produce the crosslinked elastomers of this invention may be of various types and may depend on any of several reactions to produce their crosslinking. In general, the crosslinking agents react to remove a hydrogen or halogen atom from a carbon atom on the polymer chain and thereby produce a free radical spot on the chain which is capable of linking to a similar free radical spot on another chain, either directly or indirectly. Among the crosslinking agents which may be used in this invention are the peroxy-type compounds, basic metal oxides and inorganic polysulfides. If desired, mixtures of the same or different types of crosslinking agents may be used.

The peroxy-type compounds include both organic and inorganic compounds which contain oxygen atoms directly linked to oxygen atoms. The peroxy-type compounds used in this invention must be stable below about 50 C. or else they will cause crosslinking while they are being blended into the copolymer. Among the organic compounds are the acyl and acoyl peroxide and hydroperoxides, such as ditertiary butyl peroxide, dilauryl peroxide, dibenzoyl peroxide, and ditertiary butyl hydroperoxide. The organic peroxy-type compounds also include peresters having either organic or inorganic peroxy oxygen. The former would include such compounds as alkyl and aryl perbenzoates. The latter would include alkyl and aryl persulfates.

Among the inorganic peroxy compounds are hydrogen peroxide and metal peroxides, such as lead peroxide, barium peroxide and zinc peroxide.

While it is not desired to be bound by any particular theory of operation, it is believed that the peroxy-type compounds remove a hydrogen atom from a carbon atom on the linear chain and thereby produce an activated free radical spot on the chain. This spot links directly to a similar free radical spot on another chain and thus produces a cross-linked polymer.

Among the basic oxides which may be used as linking agents are magnesium oxide, zinc oxide and lead oxide (PbO). It is believed that these basic acting compounds react with and remove a halogen atom from a carbon atom on the linear chain and produce a free radical spot on the chain. This free radical spot links directly to a similar spot on another chain and thereby produces a cross-linked polymer.

Among the inorganic polysulfides which may be used as linking agents are the alkali metal polysulfides and ammonium polysulfide. The generally accepted formula for a sodium polysulfide, for example, is Na(S) Na. It is believed that this compound breaks up into two sodium ions and a bivalent chain of sulfur atoms. Each of the sodium ions reacts with and removes a halogen atom from a linear polymer chain and leaves a free radical spot on the chain. Each end of the chain of sulfur atoms links to a free spot on a different polymer chain and thereby links the chains together.

The crosslinking reaction, with any of the above crosslinking agents, may require or may produce materials which have an adverse effect on the properties of the crosslinked polymer. For example, the metallic halides produced by the reaction of inorganic basic metal oxides with the halogen atoms of the polymer might reduce the chemical inertness and electrical resistance of the polymer. However, since relatively few crosslinkages are required to produce a substantial alteration in the characteristics of the polymer, relatively small amounts of crosslinking agents are required. In producing a crosslinked polymer for special processes where a high degree of chemical inertness or electrical resistance is required, conditions may be controlled so that a minimum of undesired material remains in the polymer.

There are several methods of reacting the linear elastomers with crosslinking agents, depending on the character of the elastomer, the character of the crosslinking agent and the character of the desired product. Crosslinking agents may be easily incorporated into the clastomers *by mechanical mixing, either with or without plasticizers. Such mechanical mixing involves shearing forces and is carried out in equipment such as 2-roll mills, Banbury (internal) mixers and screw-type plasticators, which resemble extruders. Somewhat elevated temperatures of the order of from about 50 to about C. ordinarily prevail in the mixing operation due to the mixing operation due to the mixing action itself and to the exothermic nature of the linking reaction. Articles to be molded are then heated in the mold with additional heat, as by hot air, steam or hot press platens, thereby shaping and crosslinking simultaneously. The temperature in the mold may range from about C. to 200 C.

Since mechanical mixing generates heat and since it is diificult to blend other materials into a crosslinked polymer, it is usually desirable to blend other materials into the polymer first and then add the linking agents last, just before fabrication. Among the other materials which might be added to the aforesaid polymers prior to crosslinking are fillers, pigments and plasticizers.

With certain polymers and for certain use-s, particularly for coatings, polymers may be crosslinked from solutions. The polymer and linking agents are dissolved in a suitable solvent, the solution is applied to a surface, such as a fabric or a metal, and then the coating is dried and heated to crosslink the polymer. In some cases, the coating is adherent and in other cases, it may be stripped off to form a self-supporting film of crosslinked polymer.

Still another method of crosslinking a linear polymer involves the use of a milky emulsion or latex. As stated above, the copolymerization product may be prepared in a water suspension type system. In such a system the product is removed from the reactors as a lateX. For most purposes, the dry rubbery copolymer is recovered by coagulation of the latex with salts and acids followed by washing and drying. But for other purposes, such as dip coating and spraying, the latex can be used directly. In these cases, the other ingredients (fillers, crosslinking agents, etc.) are dispersed in water containing a suface-active agent, and these dispersions are blended with the latex. The latex is then applied as a coating to a surface (similar to the solutions disclosed above) and the polymer is crosslinked as the latex is dried and heated.

Still another method of reacting the linear elastomers with a cro-sslinking agent involves the reaction of the crosslinking agent with the elastomer in its fabricated state. Since this method involves the penetration of the elastomer by the reactant crosslinking agent, it is adaptable primarily to very thin sections of elastomer, such as in coatings or in self-supporting films. The coating or film is maintained in contact with the crosslinking agent, at elevated temperatures and preferably under pressure, for a period of time ranging from about one hour to several days. This results in the vulcanization of the elastomer and in the changing of the characteristics of the linked polymer to those of a space polymer.

Example 1 One hundred parts by weight of equimolar copolymer of chlorotrifluoroethylene and vinylidene fluoride, parts by weight of a mixture of low molecular weight oily polymers of chlorotrifluoroethylene, as a plasticizer, and 15 parts by weight of benzoyl peroxide were thoroughly blended together on the cold rolls of a 2-roll mill. The blend was then press-cured for about one hour at 149 C. The cure was found to have converted the normally acetone-soluble copolymer into an insoluble product.

Example 2 One hundred parts by weight of a copolymer of chlorotrifluoroethylene and vinylidene fluoride, containing 62 mol percent of the former and 38 mol percent of the latter, 30 parts by Weight of carbon black, 2 parts by weight of stearic acid and 3 parts by weight of sodium polysulfide were thoroughly blended together on the cold rolls of a 2-roll mill. The blend was then press-cured for about one hour at 171 C. The cure was found to have converted the normally acetone-soluble copolymer into an insoluble product.

The crosslinked halogenated elastomers prepared by this invention may be used for most of the purposes for which halogenated polymers generally have been used. These elastomers have essentially the same characteristics of chemical iner-tness and insulating ability as halogenated polymers, generally, and, in addition, have the toughness and resilience associated with a vulcanized elast-omer. The crosslinked elastomers of this invention cannot be readily molded and cannot be put into solution after crosslinking. In a practical sense, however, in most cases, the cross-linking step can be performed as the final step in fabrication and thereby make subsequent solution or molding unnecessary.

Molded articles can be made, as described above, by heating and compressing a mixture of the linear elast-omer and the crosslinking agent in a mold. The articles thus produced have all of the advantages of chemical inertness of the linear halogenated elastomer, at the same time, having greater toughness and better heat stability.

Films of crosslinked halogenated elastomers, formed in situ, may be used for the protection of metallic surfaces against corrosive conditions. Such films have substantially the same chemical inertness as the films of linear elastomer, but greater toughness and better heat resistance.

The crosslinked elastomers of this invention can also be used as wire coatings since the advantageous electrical properties of the halogenated elastomers are only slightly reduced in crosslinking by the production of byproduct materials.

The crosslinked elastomers of this invention may also be used as impregnates and/or as Coatings for yarns and fabrics, including the yarns and fabrics of asbestos, glass, synthetic resins and natural fibers.

We claim:

1. An elastomeric copolymer consisting essentially of a fluorohalogenated propene in which the halogen substituents are normally gaseous halogens, not more than one of which is chlorine, and a fluorinated ethylene in which the substituents are selected from the group consisting of fluorine and hydrogen said compounds having at most two hydrogen atoms per molecule, which hydrogen atoms are in the form of CH groups, and only one of said compounds having a CH group, said copolymer having a linear carbon chain comprised of at least 10 percent -CH groups.

2. The elastomeric copolymer of claim 1 in which the linear carbon chain comprises at least 10 percent methyl side chains.

3. The elastomeric copolymer of claim 1 in which said propene is at least half halogenated.

4. The elastomeric copolymer of claim 1 in which said propene is 2-chloroperfiuoropropylene.

5. The elastomeric copolymer of claim 1 in which said propene is perfluoropropylene.

6. An elastomeric copolymer consisting essentially of perfluoropropene and a vinylidene halide in which the halogen is a normally gaseous halogen and at least one is fluorine, said copolymer having a linear carbon chain comprised of at least 10 percent -C H groups.

7. The elastomeric copolymer of claim 4 in which the linear carbon chain comprises at least 10 percent methyl side chains.

8. An elastomeric copolymer consisting essentially of hexafluoropropene and l,l-fluorochloroethylene having a carbon chain in which at least 10 percent of the carbon chains are -CH 9. The elastomeric copolymer of claim 8 in which the carbon chain comprises at least 10 percent methyl side chains.

10. The elastomeric copolymer of claim 1 in which said propene is perhalogenated.

11. An elastomeric copolymer consisting essentially of vinylidene fluoride and 2-ohloroperfluoropropylene having a carbon chain in which at least 10 percent of the carbon atoms are --CH 12. An elastomeric copolymer consisting essentially of perfluoropropylene and 1,1-fluorochlor0ethylene having a carbon chain in which at least 10 percent of the carbon atoms are CH References Cited by the Examiner UNITED STATES PATENTS 2,689,241 9/1954 Dittman et a1. 260-92.l 2,705,706 4/1955 Dittman et a1. 26092.l 3,051,677 8/ 1962 ReXford 260-87] OTHER REFERENCES Adams et al.: Journal of Polymer Science, vol. IX, 260-921, pages 481492, December 1952.

JOSEPH L. SCHOFER, Primary Examiner.

MILTON STERMAN, HAROLD N. BURSTEIN,

JOSEPH R. LIEBERMAN, PHILIP E. MANGAN,

Examiners.

J, BROWN, J. F, MCNALLY, JAMES A. SEIDLECK,

' Assistant Examiners 

1. AN ELASTOMERIC C OPOLYMER CONSISTING ESSENTIALLY OF A FLUOROHALOGENATED PROPENE IN WHICH THE HALOGEN SUBSTITUENTS ARE NORMALLY GASEOUS HALOGENS, NOT MORE THAN ONE OF WHICH IS CHLORINE, AND A FLUORINATED ETHYLENE IN WHICH THE SUBSTITUENTS ARE SELECTED FROM THE GROUP CONSISTING OF FLUORINE AND HYDROGEN SAID COMPOUNDS HAVING AT MOST TWO HYDROGEN ATOMS PER MOLECULE, WHICH HYDROGEN ATOMS ARE IN THE FORM OF CH2=GROUP, SAID COPOLYMER HAVING A LINEAR CARBON CHAIN COMPRISED OF AT LEAST 10 PERCENT -CH2-GROUPS. 